biggest role in global warming have reached their highest level in
almost 2 million years, an amount never before encountered by humans,
US scientists said on Friday.
Carbon dioxide was measured at 400 parts permillion Thursday at the
oldest monitoring station in Hawaii, which sets the global benchmark.
The number 400 has been anticipated by climate scientists and
environmental activists for years as a notable indicator, in part
because it's a round number.
"What we see today is 100 percent due to human activity," said Pieter
Tans, a senior scientist with the National Oceanic and Atmospheric
Administration. The burning of fossil fuels, such as coal for
electricity and oil for gasoline, has caused the overwhelming bulk of
the man-made increase in carbon in the air, scientists say.
At the end of the Ice Age, it took 7,000 years for carbon dioxide
levels to rise by 80 parts per million, Tans said. Because of the
burning of fossil fuels, carbon dioxide levels have gone up by the
same amount in just 55 years.
The speed of the change is the big worry, said Pennsylvania State
University climate scientistMichael Mann. If carbon dioxide levels go
up 100 parts per million over thousands or millions of years, plants
and animals can adapt. But that can't be done at the speed it isnow
happening.
The last time the worldwide carbon level was probably this high was
about 2 million years ago, Tans said. That was during the Pleistocene
Era.
"It was much warmer than it is today," Tans said. "There were forests
in Greenland. Sea level was higher, between 10 and 20 meters (33 to 66
feet)."
Other scientists say it may have been 10 million years since Earth
last encountered this level of carbon dioxide.
When measurements were first taken in 1958,carbon dioxide was measured
at 315 parts permillion. Levels are now growing about 2 partsper
million per year. That's 100 times faster than at the end of the Ice
Age.
Before the Industrial Revolution, carbon dioxide levels were around
280 ppm, and they were closer to 200 during the Ice Age.
There are natural ups and downs of the greenhouse gas, which comes
from volcanoes and decomposing plants and animals. But that's not what
has driven current levels so high, Tans said. He said the amount
should beeven higher, but the world's oceans are absorbing quite a
bit, keeping it out of the air.
Carbon dioxide traps heat just like in a greenhouse and most of it
stays in the air for about a century. Some lasts for thousands of
years, scientists say.
Last year, regional monitors briefly hit 400 ppm in the Arctic , but
those monitoring stations aren't seen as a world mark like the one at
Mauna Loa, Hawaii.
Generally carbon levels peak in May then fall slightly, so the yearly
average is usually a few parts per million lower than May levels.
